1. Field of the Invention
The present invention is related to a solid-state image capturing apparatus, an mounting method for the solid-state image capturing apparatus, a manufacturing method for the solid-state image capturing apparatus, and an electronic information device, and more particularly, to an element structure for improving the moisture resistance of a solid-state image capturing apparatus including a chip of a solid-state image capturing element (also referred to as an image capturing element chip, hereinafter) housed in an element sealing package; a method for mounting the solid-state image capturing element in such a manner to have the element structure; a method for manufacturing a solid-state image capturing apparatus that has the element structure, and an electronic information device including the solid-state image capturing apparatus that has the element structure.
2. Description of the Related Art
Conventionally, various kinds of structures with an improved moisture resistance exist as a mounting structure of a solid-state image capturing element.
FIG. 12 illustrates a solid-state image capturing apparatus having a mounting structure where a solid-state image capturing chip is sealed with resin on a ceramic substrate (see Reference 1), as an example of a conventional solid-state image capturing apparatus.
A solid-state image capturing apparatus 50 illustrated in FIG. 12 includes a ceramic substrate 51 having an external lead terminal formed on a back surface side. A solid-state image capturing element chip 52 is fixed on the ceramic substrate 51 with an adhesive, and an electrode of the image capturing element chip 52 and an electrode portion of the ceramic substrate 51 are connected to each other by a bonding wire 56. In addition, a color filter 53 is adhered on a surface of the image capturing element chip 52 with a transparent adhesive 54. In addition, exposed surfaces of the ceramic substrate 51, image capturing element chip 52, color filter 53, and bonding wire 56 are covered with a moisture-resistant silicon nitride film 55. Further, an upper surface of the ceramic substrate 51 is sealed with a sealing resin 57 in such a manner to expose a light incident surface of the color filter 53, and the image capturing element chip 52, color filter 53, and bonding wire 56 are embedded in the sealing resin 57.
Next, a mounting method will be described.
First, the image capturing element chip 52 is adhered to the ceramic substrate 51 that includes an exterior lead terminal 58; and an internal electrode (electrode pad) of the image capturing element chip 52 and the electrode portion of the ceramic substrate 51 are connected with the bonding wire 56.
Next, the color filter 53 formed with an organic material is adhered to a surface of the image capturing element chip 52 with the transparent adhesive 54.
Subsequently, the ceramic substrate 51 equipped with the image capturing element chip 52 and the color filter 53, is positioned in a plasma CVD apparatus to form a plasma silicon nitride film 55 of 400 to 500 nm on an entire surface thereof.
Further, the solid-state image capturing element chip 52 and the color filter 53 of the ceramic substrate 51 are sealed with a resin 57, and subsequently, the silicon nitride film 55 formed on an unnecessary portion of a light incident surface (upper surface) of the color filter 53, the external lead terminal 58 and the like, is removed by etching.
According to the solid-state image capturing apparatus having the mounting structure described above, an interface portion of a side surface of the solid-state image capturing chip and a side surface of the color filter, which is a infiltration path for moisture, is entirely covered with a moisture-resistant insulation film to prevent moisture from entering from the transparent adhesive portion of the interface. As a result, the solid-state image capturing apparatus prevents moisture from infiltrating into the transparent adhesive 54, which is the interface of the color filter 53 and the image capturing element chip 52, thereby preventing the deterioration (fading) of the color filter, which is composed of an organic material, and the deterioration, such as corrosion, of the image capturing element chip itself.
Among the solid-state image capturing elements in recent years, the number of pixels in the elements steadily increases. In addition, it has become a common technique to form a color filter, and further, a microlens for focusing light on the solid-state image capturing element for the purpose of compensating a decreased light receiving area per pixel.
However, the color filter is adhered on the solid-state image capturing element chip according to the mounting structure of the conventional solid-state image capturing apparatus 50 illustrated in FIG. 12. As a result, the microlens cannot be formed on the surface of the solid-state image capturing element chip, and the area for receiving light is limited only to the portion where a light shielding film is open in the solid-state image capturing element chip, resulting in a significant decrease of the sensitivity for the recent fine pixels.
For this reason, a mounting structure to seal the image capturing element chip with a sealing package and a lid glass is applied for recent image capturing element chips with a microlens, as illustrated in FIG. 13(a).
A solid-state image capturing apparatus 70 illustrated in FIG. 13(a) includes a sealing package 71 that includes an external lead terminal 77. An image capturing element chip 72 is fixed on a bottom surface inside the sealing package 71 with an adhesive 75a, and an electrode of the image capturing element chip 72 and an electrode portion of the sealing package 71 are connected to each other with a bonding wire 73.
Subsequently, a microlens 78 is formed on a surface of the image capturing element chip 72 in a corresponding manner to each pixel, and a reflection preventing film 74 is formed on the microlens 78. In addition, the sealing package 71 described above includes a package substrate 71a and an external wall portion 71b formed in the periphery of the package substrate 71a. The sealing package 71 is formed with a mold resin and ceramic.
A lid glass 76 is adhered on the external wall portion 71b, and the image capturing element chip 72 described above is sealed by the lid glass 76 and the sealing package 71 described above. In addition, a hollow space is formed between the lid glass 76 and the microlens of the image capturing element chip.
Hereinafter, a method will be described for mounting the image capturing element chip described above on a package.
First, an image capturing element wafer W2, which is formed in a former half wafer process, is cut for each image capturing element chip 72 (die), and each image capturing element chip (only the ones with good quality) is taken out (FIG. 14(a)). At this stage, a resist for protecting a surface is formed only on an image capturing area of the image capturing element chip. That is, no resist remains on an electrode pad of the image capturing element chip.
Next, a package 71 without a die mounted thereon is mounted on each mounting portion Car of a sealing process (latter half process) flowing carrier Ca (FIG. 14(b)). Herein, the flowing carrier Ca is formed to be capable of mounting 5 to 10 of the sealing packages 71 described above. Further, the sealing package 71 includes the external lead terminal 77 and the package substrate (package body) 71 as described above. A lid member for pressing and fixing the package is denoted as Ca1 in the figure.
After a model name, manufacturer name and the like are printed on a back surface of the package body (FIG. 14(c)), the image capturing element chip (die) 72 is adhered to the package 71 with the adhesive 75a (FIG. 14(d)).
Subsequently, an electrode terminal of the image capturing element chip 72 and the external lead terminal 77 are connected to each other with a gold wire 73 (FIG. 14(e)). Further, after the removal of a resist 72a for protecting the element surface (FIG. 14(f)), a UV cured resin 75b (also referred to as glass seal) is applied on an upper surface of the external wall portion 71b of the package. After the lid glass 76 is mounted on the surface of the package, the UV cured resin 75b is cured using UV radiation and the lid glass 76 is adhered on the surface of the package (FIG. 14(g)).
The element sealing method described above is an extremely ordinary method for sealing an image capturing element chip with a microlens. However, such solid-state image capturing apparatus that is sealed by the method is not sufficient for a countermeasure to prevent moisture from infiltrating and the like from the outside of the package.
That is, although it is possible to prevent a physical damage or a direct contact with moisture from the outside into the image capturing element chip by the lid glass 76 of the surface of the package and the glass seal 75b for adhering the external wall of the package and the lid glass, it is not possible to completely prevent moisture from infiltrating from the glass seal portion, which is an adhesive. In such a case, an impurity contained in the moisture or even a glass seal component is mixed with the infiltrating moisture, resulting in corrosion of metal wirings in the image capturing element chip and an occurrence of other malfunction that leads to impairing the reliability.
It is conceivable that these undesirable matters are caused because the hollow space is provided above the image capturing element chip (above the microlens). However, the following reasons are listed for the reason why the hollow space is provided above the image capturing element chip (i.e., the entire space inside the package), instead of filling it with a resin or the like.
FIG. 13(b) is a diagram illustrating a diagrammatic cross sectional structure of a pixel portion in a solid-state image capturing element (e.g., CCD image capturing element).
A silicon substrate 81, which configures the solid-state image capturing element chip 72, illustrated in FIG. 13(b) includes a photodiode 82 formed in a predetermined area, for performing a photoelectric conversion that corresponds to each pixel. In addition, a gate electrode 83 formed of a polysilicon film is formed on both sides of the photodiode 82 above the silicon substrate 81, with a gate insulation film interposed therebetween. The gate electrode is covered by a light shielding film 84. Further, color filters 87a and 87b are positioned on the silicon substrate 81 and the gate electrode 83 with a first interlayer insulation film interposed therebetween (planarizing film) 85a. Further, a microlens 86 is positioned on the color filter with the second interlayer insulation film (planarizing film) 85b interposed therebetween.
Next, a manufacturing method will be described for the image capturing element chip 72. Herein, the color filter 87a is a green color filter, and the color filter 87b is either a red or blue color filter.
First, the photodiode 82 for converting a received light into an electric charge is formed by an impurity ion planting with phosphorus or the like in an area corresponding to each pixel of the silicon substrate 81. Subsequently, the gate electrode 83 for reading out and transferring an electric charge from the photodiode is formed with a polysilicon film and the like. Subsequently, a light shielding film 84, which is for preventing light from entering an area other than the photodiode of the surface of the substrate (e.g., electric charge transferring section), is formed with a high melting point metal material, such as tungsten. Subsequently, the first planarizing film 85a for planarizing an element is formed on the entire surface with one of a silicon oxide film, a silicon nitride film and a transparent organic material, or the combination thereof.
Subsequently, each of the color filters of the respective colors is formed on the first planarizing film 85a. For example, a green color filter is first formed in an odd numbered pixel of an odd pixel row and in an even numbered pixel of an even pixel row. Next, a red color filter is formed in an even numbered pixel of an odd pixel row; and a blue color filter is formed in an odd numbered pixel of an even pixel row.
After the second planarizing film 85b is formed, the microlens 86 is formed thereon with a transparent organic film (e.g., acrylic).
Herein, it is about 3 μm to 5 μm in thickness from the surface of the silicon substrate 81 to the surface of the second planarizing film. In addition, with regard to the thickness of the color films, the green color filter is about 0.4 to 0.5 μm, each of the red and blue color filters is about 0.5 to 0.8 μm in thickness. The microlens is about 0.4 μm to 2 μm in thickness.
Note that color filters of complementary colors may be used as well, instead of the above-described color filters of primary colors such as green, red and blue.
More specifically, complementary colors, such as Cy (cyan), Mg (magenta), Ye (yellow) and Gr (green), are used for the complementary color filters. However, a Gr color filter in this case will be formed by overlapping a Cy color filter and a Ye color filter, and therefore, the color filters to be formed during the process are only the three color filters of Cy, Mg and Ye. In addition, the Ye color filter is 0.5 μm in thickness; the Mg color filter is 0.9 μm in thickness; and the Gr color filter (Cy color filter and Ye color filter) is 1.0 μm in thickness. The Cy color filter (single layer portion) is 1.0 μm in thickness.
The role of the microlens 86 is to effectively lead the light that enters the microlens into the photodiode (opening portion of the light shielding film). In that case, the relationship of the microlens and the refractive index of the above portion is extremely important. The refractive index of an acrylic material, which is an ordinary organic material, is 1.60; and the refractive index of the hollow space (air) thereabove is 1.0. Incident light is refracted and focused towards the photodiode because of the difference of the refractive indexes and the shape of the microlens. For example, if a resin or the like fills the space above the microlens, the refractive index will be about 1.60 there, which is hardly different from the refractive index of the microlens. As a result, the incident light will not be focused on the photodiode no matter what kind of shape is made for the microlens.
Therefore, for example, a similar light focusing effect can be obtained by forming the entire microlens with a silicon nitride film (refractive index of 2.0) and filling the above portion with a resin (refractive index of about 1.60). However, this method is not adopted currently because the light focusing effect obtained is the same as before despite of the difficulty in forming the element.
In addition, Reference 2 also discloses a solid-state image capturing apparatus with the mounting structure illustrated in FIG. 13.
Reference 1: Japanese Laid-Open Publication No. 4-250665
Reference 2: Japanese Laid-Open Publication No. 4-223371